LONDON - London Heathrow Airport said on Saturday that flights have resumed after the power outage and the airport is now "fully operational".

"We can confirm that Heathrow is open and fully operational today. Teams across the airport continue to do everything they can to support passengers impacted by yesterday's outage at an off-airport power substation," the airport said in a statement.

It said hundreds of additional staff have been drafted in to help clear the backlog of flights.

"We have added flights to today's schedule to facilitate an extra 10,000 passengers travelling through the airport," it added, while suggesting passengers check with their airline for the latest information regarding their flight.

The airport's chief executive Thomas Woldbye said he doesn't expect "major amounts" of delays and cancellations on Saturday, but airlines will have to deal with the passengers who were stranded as a result of disruption since the power outage.

Woldbye told the BBC that he is "sincerely sorry" for inconvenience to passengers but defended the airport's decision for closure, saying that the power substation is not part of Heathrow's infrastructure.

"We were handling the consequences of that failure," he said.

The closure of Heathrow, one of the world's busiest airports, is estimated to have disrupted the travel plans of 200,000 people, The Guardian reported.

Meanwhile, counter-terror officers from the Metropolitan Police are leading the investigation into the fire at the nearby electricity substation that has closed the airport.

A Met spokesperson said its Counter Terrorism Command was leading the investigation due to "the location of the substation and the impact this incident has had on critical national infrastructure."

There was "currently no indication of foul play", but the spokesperson added that officers were retaining an "open mind at this time" regarding the cause of the blaze.

Flights had been canceled, people evacuated from their homes, and local schools shut after two explosions and a fire at an electrical substation in Hayes, west London, on Thursday night. Some planes had been diverted to other airports, including London Gatwick Airport, those in Paris, and Shannon Airport in Ireland.

The airport, which handled a record 83.9 million passengers last year, said its back-up diesel generators had "all operated as expected... but they are not designed to allow us to run a full operation".

Ofgem, Britain's energy regulator, announced it would commission a review "to understand the cause of this incident and what lessons can be learned".